Exposure method

ABSTRACT

An exposure method for transferring a pattern on a mask onto a photosensitive substrate. The exposure method has steps of (1) preparing the mask with a first alignment mark and the substrate with a second alignment mark, a length of the first alignment mark in a scan direction being shorter than a length of the second alignment mark in the same direction; (2) scanning the first and second alignment marks; (3) detecting an intensity of the light which has been emitted from the light source optical system and irradiated the mask and the substrate; (4) calculating an amount of dislocation between the first and second alignment marks in the scan direction; (5) correcting the dislocation between the mask and the substrate; (6) effecting an exposure to transfer the pattern on the mask onto the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exposure method, in particular,which is preferably adopted as such an apparatus having a positioningmechanism for a mask and a photosensitive substrate.

2. Related Background Art

Conventionally, in the exposure apparatus using the exposure method ofthis type, a positioning mechanism having a structure such as that shownin FIG. 1 has been used in general. The basic action of this exposureapparatus 1 comprises the steps of irradiating an alignment mark 3A of amask 3 and an alignment mark 4A of a photosensitive substrate 4, whichare disposed so as to sandwich a projection optical system 2therebetween, with alignment light; detecting the resulting diffractedlight components to determine the positional relationship between themask 3 and the photosensitive substrate 4; and then, on the basis of theresult of detection, adjusting the positional relationship between themask 3 and the photosensitive substrate 4.

The alignment light, which has been shaped into a predetermined form atthe time when emitted from a light source optical system 5, is projectedon the mask 3 by way of a movable mirror 6, an alignment optical system35, and a fixed mirror 7. The alignment light passing through the mask 3is projected on the photosensitive substrate 4 by way of the projectionoptical system 2.

The movable mirror 6 herein is positioned such that it can be moved in adirection of arrow A by a mirror-driving portion 6A. Along the movementof the movable mirror 6, the mask 3 and the photosensitive substrate 4are scanned with the alignment light thereon. The position of themovable mirror 6, meanwhile, is monitored by a mirror-position detector(interferometer, encoder, or the like) 8.

When the alignment light overlaps with each mark at the time ofscanning, the alignment light is scattered by the mark. In the exposureapparatus 1, the scattered light component (i.e. diffracted lightcomponent) is taken out by way of a half mirror 9 and a spatial filter10 and then converted to an electric signal by a photodetector 11.Thereafter, on the basis of the positional information obtained by themirror-position detector 8 and the light intensity signal obtained bythe photodetector 11, the relative positions of the mask 3 and thephotosensitive substrate 4 with respect to each other are calculated anddetermined by a mark-position calculating means 12.

FIG. 2 shows how the position of the alignment mark 4A formed on thephotosensitive substrate 4 is detected. As shown in this drawing, thescattered light component from the alignment mark 4A passes through themask 3 again and then is taken out by the half mirror 9 so as to betransmitted to the spatial filter 10. The spatial filter 10, meanwhile,has such a structure that the zero-order light component is cut off soas to transmit only the scattered light component to the photodetector11.

Similarly, FIG. 3 shows how the position of the alignment mark 3A formedon the mask 3 is detected. As shown in this drawing, the scattered lightcomponent generated by the alignment mark 3A is taken out by the halfmirror 9 so as to be transmitted to the spatial filter 10 and thephotodetector 11. At this moment, the detection signal which is inputinto the mark-position calculating means 12 from the photodetector 11has a wave form in which, as shown in FIG. 4, the position of its peakscorrespond to the positions of the marks to be detected.

These two peaks are formed because, as the scattered light componentfrom the alignment mark 4A is detected after passing through the mask 3,the alignment mark 4A and the alignment mark 3A have been positionedwith a distance x therebetween so as not to overlap with each other.However, as the detected signal includes an amount of dislocation, adifference of x+Δx (wherein Δx is the amount of dislocation of themarks) is detected between the signal corresponding to the alignmentmark 4A on the photosensitive substrate side and that corresponding tothe alignment mark 3A on the mask side. The amount of dislocation Δx caneasily be calculated from the result of measurement since x is known.

SUMMARY OF THE INVENTION

In the exposure method in accordance with the present invention, while afirst alignment mark disposed on a mask and a second alignment markdisposed on a photosensitive substrate are irradiated with a luminousflux, the first and second alignment marks are relatively scanned withthe luminous flux and the positional relationship between the first andsecond alignment marks is detected by a position detector on the basisof optical information obtained from the first and second alignmentmarks. The second alignment mark is disposed on the photosensitivesubstrate at a position which is substantially conjugate with the firstalignment mark and has a length in the scan direction longer than thatof the first alignment mark. The first and second alignment marks arescanned with the luminous flux substantially simultaneously and therebythe position detector detects the positional relationship between thefirst and second alignment marks.

Preferably, there is further provided a driving mechanism for driving atleast one of the mask and the photosensitive substrate so as to correctthe relative relationship between the mask and the photosensitivesubstrate.

Preferably, the first alignment mark is a light-shielding mark.

In accordance with one aspect of the present invention, the exposureapparatus is provided with an illumination optical system forirradiating the photosensitive substrate with the luminous flux by wayof the mask, while the position detector has a light-receiving portionfor detecting, in the reflected light from the second alignment mark,the luminous flux passing through a periphery of the first alignmentmark as the optical information.

In accordance with another aspect of the present invention, the exposureapparatus is provided with an illumination optical system forirradiating the photosensitive substrate with the luminous flux not byway of the mask, while the position detector has a light-receivingportion for detecting, in the reflected light from the second alignmentmark, the luminous flux passing through a periphery of the firstalignment mark as the optical information.

In the present invention, since the first alignment mark and the secondalignment mark are disposed near positions which are substantiallyconjugate with and correspond to each other, the positional signals ofthe first and second alignment marks can be detected simultaneously andindependently when scanned once with the luminous flux.

As the positional signals respectively corresponding to two marks can beobtained at the same time in this manner, errors caused by distortion ofthe alignment optical system can be eliminated. Also, as the positionalsignals of the first and second alignment marks can independently bedetected, the processing for adjusting the gains of the positionalsignals obtained by two separate scans with the luminous flux can beeliminated. As a result, it is possible to obtain an exposure methodwhich can further improve the positioning accuracy while improving thethroughput.

Further, since the length of the second alignment mark in the scandirection is made longer than that of the first alignment mark in thescan direction, these marks can be disposed at positions which areconjugate with and correspond to each other.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will beapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagrammatic side view showing a conventionalexposure apparatus;

FIGS. 2-4 are schematic diagrammatic views showing the conventionalexposure apparatus and a signal intensity distribution detected thereby;

FIG. 5 is a schematic diagrammatic side view showing an exposureapparatus in accordance with an embodiment of the present invention;

FIG. 6 is a schematic diagrammatic side view explaining the scanning ofalignment marks with alignment light;

FIGS. 7-9 are schematic diagrammatic views showing a light intensitydistribution corresponding to a relationship between an alignment markon a mask and that on a photosensitive substrate;

FIG. 10 is schematic diagrammatic view explaining a step for detectingan amount of dislocation;

FIG. 11 is a schematic diagrammatic side view showing an exposureapparatus in accordance with another embodiment of the presentinvention; and

FIG. 12 is a flowchart showing an exposure method of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the above-mentioned conventional technique, errors may occur in theresult of detection due to distortion of the alignment optical system35, since the alignment mark 3A and the alignment mark 4A have beendisposed so as to keep away from each other. This is because theluminous flux from the alignment mark 3A and that from the alignmentmark 4A respectively pass through different parts within the alignmentoptical system 35.

Also, while chromium (Cr) is generally used for the alignment mark 3A onthe mask, various materials from a low-reflectance film of ITO or thelike to a high-reflectance film of aluminum (Al) or the like are usedfor the alignment mark 4A on the photosensitive substrate. Accordingly,the scattered light intensity on the mask and that on the photosensitivesubstrate often differ greatly from each other. Thus, it is necessaryfor the marks to be separately subjected to automatic gain controlprocessing in order to attain substantially the same level of lightintensity. As a result, it is necessary for the taken-out signals to bedivided into separate scans, thereby inevitably lowering the throughputand deteriorating the accuracy in measurement.

FIG. 5 is a side view showing an embodiment of the present invention. InFIG. 5, the parts corresponding to those depicted in FIG. 1 are referredto by the same reference numerals. In FIG. 5, reference numeral 20indicates an exposure apparatus as a whole. In this apparatus 20,alignment marks 21 and 22 are disposed at positions which are conjugatewith and correspond to each other with respect to the projection opticalsystem 2. Namely, the alignment mark 22 is disposed near a position onthe photosensitive substrate 4 which is equivalent to the position ofthe alignment mark 21 on the mask 3. Accordingly, when (relatively)scanned once with alignment light, the relative positional relationshipbetween the mask 3 and the photosensitive substrate 4 can be detected.The light source optical system 5 for the alignment light emits laser.

The alignment mark 22 formed on the photosensitive substrate 4 has asize with respect to the scan direction of alignment light (i.e.,direction of arrow B in FIG. 5) longer than that of the alignment mark21 formed on the mask 3 with respect to the same direction. The shapesand the like of the alignment marks 21 and 22 are as explained in thefollowing. Namely, on a transparent portion such as glass, the alignmentmark 21 on the mask is formed as a light-shielding portion (i.e.,chromium pattern) which is the same as or slightly larger than the crosssection of the alignment light such that, the alignment mark 22 isirradiated with the alignment light passing through the transparentportion outside of the alignment mark 21. On the other hand, thealignment mark 22 on the photosensitive substrate comprises agrating-like mark formed by an etched metal film or semiconductor filmsuch that scattering (diffraction) is likely to occur at the mark.

Thus, the alignment mark 21 on the mask merely partially blocks theincident alignment light. In this embodiment, only the scattered lightcomponent generated at the alignment mark 22 formed on thephotosensitive substrate is detected to determine the positions of thealignment marks 21 and 22. Accordingly, unlike the conventionaltechnique, it is not necessary to divide the alignment light scan andadjust the difference in light intensity depending on whether thealignment mark is on the mask or on the photosensitive substrate.

In the structure explained above, the exposure method will be explainedwith reference to FIGS. 5-10 and 12. First, as shown in FIG. 5, the mask3 on which the alignment mark 21 has been formed is mounted on a maskstage 36, whereas the photosensitive substrate 4 is mounted on asubstrate stage 37 (step S1 in FIG. 12). The alignment mark 22 has beenformed on the photosensitive substrate 4 in the preceding steps. Then,as shown in FIG. 6, the movable mirror 6 is moved in the direction ofthe arrow C (a→b→c) so that the alignment marks 21 and 22 are relativelyscanned with the alignment light (step S2 in FIG. 12). At this moment,the optical axis of the alignment light moves in the direction ofa'→b'→c' along the movement of the movable mirror 6. Accordingly, achange in light intensity such as that shown in FIG. 9 is detected atthe photodetector 11 (step S3 in FIG. 12).

This change in light intensity is obtained as explained in thefollowing. Namely, for some time after the start of scan, the alignmentlight impinges on a periphery area (i.e., transparent portion), on whichthe alignment mark 21 has not been formed, and passes through the mask 3to irradiate the photosensitive substrate 4 while moving thereon. Then,the alignment light passing through the mask 3 moves onto the alignmentmark 22 formed on the photosensitive substrate 4 (i.e., position wherethe optical axis is at a'), whereby the scattered light componentscattered (diffracted) on the mark is detected by the photodetector 11.

When the scan with the alignment light is further continued, thealignment light comes to irradiate the alignment mark 21 formed on themask 3 (i.e., position where the optical axis is at b'), while thealignment light passing through the mask 3 to reach the photosensitivesubstrate 4 is gradually shielded by the alignment mark 21. Accordingly,the light intensity of the scattered light component from the alignmentmark 22 gradually decreases so as to yield a trough in the detectionoutput of the photodetector 11.

This condition continues until the alignment light moves to an edgeportion of the alignment mark 21. Then, when the position of incidenceof the alignment light moves again to the periphery area (i.e.,transparent portion) where the alignment mark 21 has not been formed(i.e., position where the optical axis is at c'), the scattered lightcomponent from the alignment mark 22 is detected by the photodetector 11again, thereby increasing the light intensity again. When the alignmentlight further moves to the portion where the alignment mark 22 has notbeen formed, the light intensity decreases again to zero.

In this manner, the light intensity distribution corresponding to thepositional relationship between the alignment mark 21 on the mask andthe alignment mark 22 in the photosensitive substrate, i.e., includingthe positional information on the alignment mark 21 and the positionalinformation on the alignment mark 22, is detected by a mark-positioncalculating means 23. The mark-position calculating means 23 detects, onthe basis of the first-order differential wave form of the signalcorresponding to the light intensity distribution, an amount ofdislocation ΔW generated in the alignment marks 21 and 22.

For example, when the alignment mark 21 on the mask is dislocated towardthe upstream of the alignment light scan direction with respect to thealignment mark 22 on the photosensitive substrate as shown in FIG. 8,the earlier peak in the two peak wave forms becomes thinner while thelater peak becomes thicker as shown in the graph of FIG. 9 or 10. Theaxis of abscissa of FIG. 9 corresponds to the position of scan with thealignment light shown in FIG. 7. In this case, since the peak points ofthe first-order differential wave form shown in the lower graph of FIG.10 correspond to the edge portions of the alignment marks 21 and 22, themark-position calculating means 23 determines, on the basis of thepositional information obtained from the mirror-position detector 8,positions d, e, f, and g which provide the peak points of the firstdifferential wave form and then calculates the amount of dislocation ΔWaccording to the following equation (step S4 in FIG. 12): ##EQU1## Afterthe amount of dislocation is calculated in this manner, this amount ofdislocation ΔW is used to relatively move the mask 3 or thephotosensitive substrate 4 to correct the positional dislocation (stepS5 in FIG. 12), thereby effecting the exposure under a condition wherethere is no dislocation of the pattern so as to transfer the pattern ofthe mask 3 to the photosensitive substrate 4 (step S6 in FIG. 12).

In the structure explained above, since the amount of dislocation ΔWbetween the alignment marks 21 and 22 can be calculated by only one scanwith the alignment light, an exposure apparatus yielding a throughputwhich is much higher than that conventionally obtained can be realized.

Also, since the alignment mark 21 on the mask and the alignment mark 22on the photosensitive substrate can be disposed in a conjugaterelationship with each other with respect to the projection opticalsystem 2, the positional errors resulting from distortion of theprojection optical system and the like can be eliminated as much aspossible, thereby attaining an accuracy in detection much higher thanthat conventionally obtained.

Though the foregoing embodiment explains a case where the alignmentlight emitted from the light source optical system 5 impinges on theupper surface of the mask 3 and the alignment light passing through theprojection optical system 2 impinges on the photosensitive substrate 4,the present invention is not restricted thereto but also applicable to acase where the alignment light is introduced between the projectionoptical system 2 and the photosensitive substrate 4 to directly impingeon the photosensitive substrate 4. An example of the latter case isshown in FIG. 11 with the same reference numerals being applied to theparts corresponding to those of FIG. 5.

In this exposure apparatus 30, the alignment light is guided onto thealignment mark 22 on the photosensitive substrate 4 by the half mirror 9and the scattered light thereon is detected by way of the projectionoptical system 2 and the mask 3. In this case, however, the alignmentmark 21 on the mask does not prevent the alignment light from reachingthe photosensitive substrate 4 but prevents the scattered light fromreaching the photodetector 11.

When input in this manner, the alignment light passes through theprojection optical system 2 only once. Accordingly, its loss in quantityof light is smaller than that in the above-mentioned embodiment.

Further, though the embodiments of FIGS. 5 and 11 explain cases wherethe alignment mark 21 on the mask and the alignment mark 22 on thesubstrate are formed as shown in FIG. 8, they may be formed in othermanners as long as the length of the alignment mark on thephotosensitive substrate in the alignment light scan direction is madelonger than that of the alignment mark on the mask in the samedirection.

From the invention thus described, it will be obvious that the inventionmay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedfor inclusion within the scope of the following claims.

The basic Japanese Application No. 270379/1994 (6270379) filed on Oct.7, 1994 is hereby incorporated by reference.

What is claimed is:
 1. An exposure apparatus for transferring a patternon a photosensitive substrate, comprising:a mask stage which holds amask on which said pattern and a first alignment mark are formed, saidfirst alignment mark being a light shielding type mark; a substratestage which holds said photosensitive substrate having a secondalignment mark longer in a predetermined direction that said firstalignment mark so that said second alignment mark is corresponding tosaid first alignment mark; a scanning mechanism which scans a light beamalong said predetermined direction so as to traverse at least said firstalignment mark, said second alignment mark being illuminated with saidlight beam which passes near said first alignment mark in a scanning ofsaid scanning mechanism; a first detector which detects said light beamreflected on said second alignment mark; and an operating unit whichcalculates an amount of dislocation between said make and saidphotosensitive substrate.
 2. An exposure apparatus according to claim 1,further comprising: a driving unit for driving at least one of said maskstage and said substrate stage on the basis of a calculated result ofsaid operating unit to correct the relative positional relationshipbetween said mask and said substrate.
 3. An exposure apparatus accordingto claim 1, wherein a shape of said light beam is determined dependingon that of said first alignment mark.
 4. An exposure apparatus accordingto claim 3, wherein an illuminated size of said light beam is smallerthan a size of said first alignment mark.
 5. An exposure apparatusaccording to claim 1, wherein said first alignment mask blocks off saidlight beam when said light beam is on said first alignment mark and saidfirst detector does not substantially detect said light beam from saidsecond alignment mark.
 6. An exposure apparatus according to claim 1,wherein a plurality of said second alignment marks are formed along adirection substantially perpendicular to said predetermined direction.7. An exposure apparatus according to claim 1, wherein said scanningmechanism has an optical member and said scanning of said beam isperformed by movement of said optical member.
 8. An exposure apparatusaccording to claim 7, further comprising: a second detector whichdetects a position of said optical member.
 9. An exposure apparatusaccording to claim 1, wherein scanning of said scanning mechanism isperformed only one time for obtaining said amount of dislocation.
 10. Analignment method comprising the steps of:arranging a mask on which apattern and a first alignment mark of a light shielding type are formed;arranging a photosensitive substrate having a second alignment with alength longer in a predetermined direction than that of said firstalignment mark so that said second alignment mark is corresponding tosaid first alignment mark; scanning light beam along said predetermineddirection so as to traverse at least said first alignment mark, saidsecond alignment mark being illuminated with said light beam whichpasses near said first alignment mark in a scanning of said scanningstep; detecting said light beam reflected on said second alignment mark;obtaining an amount of dislocation between said mask and saidphotosensitive substrate on the basis of a detected result obtained insaid detecting step; and adjusting the relative position between saidmask and said photosensitive substrate on the basis of said amount ofdislocation.
 11. An alignment method according to claim 10, wherein ashape of said light beam is determined depending on a shape of saidfirst alignment mark.
 12. An alignment method according to claim 11,wherein a size of said light beam is smaller than that of said firstalignment mark.
 13. An alignment method according to claim 10, wherein aplurality of said second alignment marks are formed along a directionsubstantially perpendicular to said predetermined direction.
 14. Analignment method according to claim 10, wherein only one scanning isperformed for obtaining the amount of dislocation.